The present invention concerns a friction stir welding tool for friction welding.
A friction welding process is described, for example, in international publication WO 95/26254 A1. To produce a good welded connection, this publication discloses guiding a friction stir welding tool with vertical pressure along the connecting point of the workpiece to be welded. It is particularly advantageous to provide the friction stir welding tool with a concave shoulder and a pin configured in a screw shape.
Also of great importance in friction stir welding is the adjustment of a temperature that is suitable for the welding procedure in the stirred material of the weld zone. This temperature is influenced, among other things, by the parameters of the welding process, such as the rate of feed, the number of revolutions, and the contact pressure of the friction stir welding tool. Also known is a process of influencing by means of cooling devices if necessary.
It is known in friction stir welding to measure the temperature in the stirred material of the weld zone in order to control the welding procedure in accordance with the measured temperature values.
One known measuring process consists of recording the temperature of the welded plates in the vicinity of the weld zone. Since the plates cool off considerably a short distance from the weld zone, the temperature of the stirred material of the weld zone cannot be determined with sufficient accuracy with this measuring process.
Another known measuring method for determining the weld zone temperature consists of using a pyrometer. As an optical radiation measurement, this measuring method is impaired in its measurement accuracy by the structured surface of the welding location.
Such pyrometers are also used for the online monitoring of the quality of roll welding joints or mash seam welding joints as is described, for example, in European publication EP 1 075 892 A2.
One object of the invention is to create a friction stir welding tool for friction welding that can be controlled with sufficient measuring accuracy based upon the temperature in the weld zone.
This object is attained in accordance with the invention. Further developments of the invention are also disclosed.
In the temperature measuring process of the invention, the temperature of the weld zone is recorded by means of a temperature measuring device whose measuring element is arranged in the pin of the friction stir welding tool.
The measurement location is separated from the weld zone only by the thermally conductive wall of the pin, and a good correspondence can therefore be achieved between the measured and the actual temperature values of the weld zone.